Intriguing magnetism of the topological kagome magnet TbMn_6Sn_6

Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several kagome magnets have appeared as the most promising platforms. Here, we explore magnetic correlations in the transition-metal-based kagome magnet TbMn$_{6}$Sn$_{6}$ using muon spin rotation, combined with local field analysis and neutron diffraction. Our results show that the system exhibits an out-of-plane ferrimagnetic structure $P6/mm'm'$ (comprised by Tb and Mn moments) with slow magnetic fluctuations below $T_{\rm C2}$~=~320~K. These fluctuations exhibit a slowing down below $T_{\rm C1}^{*}$~${\simeq}$~120~K, and we see the formation of static patches with ideal out-of-plane order below $T_{\rm C1}$~${\simeq}$~20~K which grow in a volume with decreasing temperature. The appearance of the static patches has a similar onset to the interesting phenomenon such as spin-polarized Dirac dispersion with a large Chern gap and topological edge states. We further show that the temperature evolution of the anomalous Hall conductivity (AHC) is strongly influenced by the low temperature magnetic crossover. Our presented experimental results show that the onset of the topological electronic properties tied to the Dirac band is promoted only by true static out-of-plane ferrimagnetic order in TbMn$_{6}$Sn$_{6}$ and is washed out by the slow magnetic fluctuations above $T_{\rm C1}$~${\simeq}$~20~K. Remarkably, hydrostatic pressure of 2.1 GPa stabilises static out-of-plane topological ferrimagnetic ground state in the whole volume of the sample. Therefore the exciting perspective arises of a magnetic system in which the topological response can be controlled, and thus explored, over a wide range of parameters.
Comment: 21 pages, 12 figures